Djuzenova Cholpon S, Fiedler Vanessa, Katzer Astrid, Michel Konstanze, Deckert Stefanie, Zimmermann Heiko, Sukhorukov Vladimir L, Flentje Michael
Department of Radiation Oncology, University Hospital of Würzburg, Würzburg, Germany.
Fraunhofer-Institut für Biomedizinische Technik, St. Ingbert and Lehrstuhl für Molekulare und Zelluläre Biotechnologie/Nanotechnologie, Universität des Saarlandes, Saarbrücken, Germany.
Oncotarget. 2016 Jun 21;7(25):38191-38209. doi: 10.18632/oncotarget.9501.
Inhibition of Hsp90 can increase the radiosensitivity of tumor cells. However, inhibition of Hsp90 alone induces the anti-apoptotic Hsp70 and thereby decreases radiosensitivity. Therefore, preventing Hsp70 induction can be a promising strategy for radiosensitization. PI-103, an inhibitor of PI3K and mTOR, has previously been shown to suppress the up-regulation of Hsp70. Here, we explore the impact of combining PI-103 with the Hsp90 inhibitor NVP-AUY922 in irradiated glioblastoma and colon carcinoma cells. We analyzed the cellular response to drug-irradiation treatments by colony-forming assay, expression of several marker proteins, cell cycle progression and induction/repair of DNA damage. Although PI-103, given 24 h prior to irradiation, slightly suppressed the NVP-AUY922-mediated up-regulation of Hsp70, it did not cause radiosensitization and even diminished the radiosensitizing effect of NVP-AUY922. This result can be explained by the activation of PI3K and ERK pathways along with G1-arrest at the time of irradiation. In sharp contrast, PI-103 not only exerted a radiosensitizing effect but also strongly enhanced the radiosensitization by NVP-AUY922 when both inhibitors were added 3 h before irradiation and kept in culture for 24 h. Possible reasons for the observed radiosensitization under this drug-irradiation schedule may be a down-regulation of PI3K and ERK pathways during or directly after irradiation, increased residual DNA damage and strong G2/M arrest 24 h thereafter. We conclude that duration of drug treatment before irradiation plays a key role in the concomitant targeting of PI3K/mTOR and Hsp90 in tumor cells.
抑制热休克蛋白90（Hsp90）可增加肿瘤细胞的放射敏感性。然而，单独抑制Hsp90会诱导抗凋亡的热休克蛋白70（Hsp70），从而降低放射敏感性。因此，阻止Hsp70的诱导可能是一种有前景的放射增敏策略。PI-103是一种磷脂酰肌醇-3-激酶（PI3K）和哺乳动物雷帕霉素靶蛋白（mTOR）的抑制剂，先前已被证明可抑制Hsp70的上调。在此，我们探讨了在照射的胶质母细胞瘤和结肠癌细胞中，将PI-103与Hsp90抑制剂NVP-AUY922联合使用的影响。我们通过集落形成试验、几种标记蛋白的表达、细胞周期进程以及DNA损伤的诱导/修复来分析细胞对药物照射处理的反应。尽管在照射前24小时给予PI-103可轻微抑制NVP-AUY922介导的Hsp70上调，但它并未引起放射增敏作用，甚至削弱了NVP-AUY922的放射增敏效果。这一结果可以通过照射时PI3K和细胞外信号调节激酶（ERK）途径的激活以及G1期阻滞来解释。与之形成鲜明对比的是，当两种抑制剂在照射前3小时加入并在培养中保持24小时时，PI-103不仅发挥了放射增敏作用，还强烈增强了NVP-AUY922的放射增敏效果。在这种药物照射方案下观察到放射增敏的可能原因可能是在照射期间或照射后直接下调PI3K和ERK途径、增加残留DNA损伤以及24小时后强烈的G2/M期阻滞。我们得出结论，照射前药物治疗的持续时间在肿瘤细胞中同时靶向PI3K/mTOR和Hsp90方面起着关键作用。
